Did a quick search on this thread and saw a couple of people mention using iPads. Would love to trade notes on what you guys are using to do that. I have a central computer running WMC 7, and a few XBox 360's. I also have iPhones, iPads, and Apple TV2's (and an ATV3). The XBox 360 as extender works great - can use the guide and watch live TV.
For the iPhone/iPad, I've experimented with the following:
1) RemotePotato app. Can control the guide, see the metadata on the shows you've recorded, and stream them, including shows which are still recording. Can't do live TV, but you can record something new and start streaming it about 5 mins later, so that's pseudo-live. My problems with it, though, are that it's buggy and the video quality is sub-par (at the higher bitrates, it stutters and still doesn't look as good as AirVideo, and at the lower bitrates it just looks awful all around).
2) AirVideo app. No guide, live TV, or metadata info, but you can point the desktop app to the Recorded TV folder, view the files on your iPhone and play them with very high quality video. You can Airplay them to an ATV2/3, but on a larger screen you may notice video degradation and the framerate can feel less than smooth.
3) MC-TVConverter. This is an app that runs on your computer and can convert copy-freely shows to MP4. The app is more of a shell to a bunch of other apps (including Handbrake). Resulting video quality is the best, and you can end up with small files that you can save forever and take with you on-the-go. It can be configured to watch the Recorded TV folder and start transcoding a show as soon as its done recording, or it can run at a set time (e.g., in the middle of the night) to convert things. You can't do live TV, of course. With a fast computer, a 1/2 hour show, could be transcoded in 2x speed, so it could be ready to watch 15-30 minutes after the live show has finished.
Most of the above I've experimented with but not had any major need for. AirVideo and Remote Potato support over-the-internet streaming as well, but I'm picky about quality and suspect that I wouldn't be satisfied with Remote Potato's PQ, given my experience with its PQ when streaming inside my house.
I'd love for Apple to release a next-gen AirportExtreme/TimeCapsule that ran iOS and had a DVR server that could interface with the PRIME and do on-the-fly MP4 conversion (and record shows in that format), so as to support live TV viewing on any iOS device, including support for the ATV2/3, of course. Then I could ditch the XBox 360's and have the more invisible ATV3 as my main set top box. But I suspect that Apple has more interest in growing their iTunes pay-per-show model.
Any other interesting solutions for streaming live TV to an iPhone/iPad/ATV I may have missed?